Rapid ceramic matrix composite fabrication of  aircraft brakes via field assisted sintering

ABSTRACT

A method of making a ceramic matrix composite (CMC) brake component may include the steps of applying a pressure to a mixture comprising ceramic powder and chopped fibers, pulsing an electrical discharge across the mixture to generate a pulsed plasma between particles of the ceramic powder, increasing a temperature applied to the mixture using direct heating to generate the CMC brake component, and reducing the temperature and the pressure applied to the CMC brake component. The ceramic powder may have a micrometer powder size or a nanometer powder size, and the chopped fibers may have an interphase coating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims priority to,U.S. application Ser. No. 15/596,770 filed May 16, 2017 and titled“RAPID CERAMIC MATRIX COMPOSITE FABRICATION OF AIRCRAFT BRAKES VIA FIELDASSISTED SINTERING,” which is hereby incorporated by reference in itsentirety.

FIELD

The disclosure relates generally to making aircraft brake componentsusing field assisted sintering technique (FAST).

BACKGROUND

Carbon/carbon (C/C) composites are used in the aerospace industry foraircraft brake heat sink materials. Silicon carbide (SiC) based ceramicmatrix composites (CMCs) have found use as brake materials in automotiveand locomotive applications. These composites are typically producedusing one or more of these three main methods: chemical vaporinfiltration (CVI), melt infiltration (MI), and polymer impregnation andpyrolysis (PIP). However, each of these CMC fabrication methods haslimitations. The processing time for both CVI and PIP, for example, canextend well over 100 hours. MI generated CMCs tend to contain residualsilicon, which limits upper use temperature. Thus, existing processestypically run too long and/or have imprecise stoichiometric control foraerospace.

SUMMARY

A method of making a ceramic matrix composite (CMC) brake component isprovided according to various embodiments. The method may include thesteps of increasing a pressure in a mold containing a mixture comprisinga ceramic powder and fibers, pulsing an electrical discharge across themixture to generate a pulsed plasma between particles of the ceramicpowder, and increasing a temperature in the mold using direct heating togenerate the CMC brake component. The temperature and pressure appliedto the CMC brake component may be reduced to complete the process.

In various embodiments, suitable ceramic powders may have a range ofsizes on the order of micrometer powder size and/or a nanometer powdersize. The ceramic powder may include SiC, B₄C, and/or Si₃N₄, TiB₂, orother oxides and/or borides, for example. The fibers may be choppedcarbon fibers, chopped SiC fibers, chopped glass fibers, or choppedoxide fibers, for example. The mold may be made from graphite,refractory metals, and/or ceramics. The CMC brake component may bemachined to form precise contours and/or openings. The direct heatingmay be accomplished using resistance heating and/or inductive heating.The CMC brake component may be a CMC brake disc, for example. Thetemperature applied to the mixture may increase a maximum temperature ofabout 2400° C. The pressure may be increased by actuating a punch topress against the mixture. The electrical discharges may be pulsedacross the mixture through a graphite electrode coupled to the punch, abrass electrode coupled to the graphite electrode, and a copper platecoupled to the brass electrode. The electrical discharges may also bepulsed at a cycle time of substantially 10 minutes. The fibers may havean interphase coating made of, for example, pyrolytic carbon or boronnitride.

The method of making a CMC brake component may also include the steps ofapplying a pressure to a mixture comprising ceramic powder and choppedfibers, pulsing electrical discharges across the mixture to generate apulsed plasma between particles of the ceramic powder, increasing atemperature applied to the mixture using direct heating to generate theCMC brake component, and reducing the temperature and the pressureapplied to the CMC brake component. The ceramic powder may have amicrometer powder size or a nanometer powder size, and the choppedfibers may have an interphase coating.

In various embodiments, the ceramic powder may include SiC, B₄C, and/orSi₃N₄, oxides, and/or borides. The chopped fibers comprise at least oneof chopped carbon fiber, chopped SiC fiber, chopped glass fiber, and/orchopped oxide fiber. The interphase coating may include pyrolytic carbonor boron nitride.

A CMC brake component for an aircraft is also provided. The CMC brakecomponent may include an annular disc. The annular disc may include aceramic material having a monolithic grain structure and comprising SiC,B₄C, and/or Si₃N₄. Chopped fibers may be dispersed within the ceramicmaterial and may have an interphase coating. The chopped fibers may alsoinclude chopped carbon fiber, chopped SiC fiber, chopped glass fiber,and/or chopped oxide fiber.

The forgoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated hereinotherwise. These features and elements as well as the operation of thedisclosed embodiments will become more apparent in light of thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A illustrates a cross-sectional view of an exemplary aircraftbrake system comprising various brake components, in accordance withvarious embodiments;

FIG. 1B illustrates a cutaway view of an exemplary aircraft brake systemcomprising various brake components, in accordance with variousembodiments;

FIG. 2 illustrates a schematic diagram of a FAST device for generatingbrake components using a FAST process, in accordance with variousembodiments;

FIG. 3A illustrates an exemplary process for generating CMC brakecomponents, in accordance with various embodiments; and

FIG. 3B illustrates a process of generating CMC brake componentsrelative to time, in accordance with various embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the disclosures, it should be understood that other embodimentsmay be realized and that logical, chemical, and mechanical changes maybe made without departing from the spirit and scope of the disclosures.Thus, the detailed description herein is presented for purposes ofillustration only and not of limitation. For example, the steps recitedin any of the method or process descriptions may be executed in anyorder and are not necessarily limited to the order presented.Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

With initial reference to FIGS. 1A and 1B, an aircraft wheel brakingassembly 10 that may be found on an aircraft is shown, in accordancewith various embodiments. Aircraft wheel braking assembly may, forexample, comprise a bogie axle 12, a wheel 14 including a hub 16 and awheel well 18, a web 20, a torque take-out assembly 22, one or moretorque bars 24, a wheel rotational axis 26, a wheel well recess 28, anactuator 30, multiple brake rotors 32, multiple brake stators 34, apressure plate 36, an end plate 38, a heat shield 40, multiple heatshield sections 42, multiple heat shield carriers 44, an air gap 46,multiple torque bar bolts 48, a torque bar pin 50, a wheel web hole 52,multiple heat shield fasteners 53, multiple rotor lugs 54, and multiplestator slots 56. FIG. 1B illustrates a portion of aircraft wheel brakingassembly 10 as viewed into wheel well 18 and wheel well recess 28.

Brake disks (e.g., interleaved rotors 32 and stators 34) are disposed inwheel well recess 28 of wheel well 18. Rotors 32 are secured to torquebars 24 for rotation with wheel 14, while stators 34 are engaged withtorque take-out assembly 22. At least one actuator 30 is operable tocompress interleaved rotors 32 and stators 34 for stopping the aircraft.In this example, actuator 30 is shown as a hydraulically actuatedpiston, but many types of actuators are suitable, such as anelectromechanical actuator. Pressure plate 36 and end plate 38 aredisposed at opposite ends of the interleaved rotors 32 and stators 34.Rotors 32 and stators 34 can comprise any material suitable for frictiondisks, including ceramics or carbon materials, such as a carbon/carboncomposite.

Through compression of interleaved rotors 32 and stators 34 betweenpressure plates 36 and end plate 38, the resulting frictional contactslows rotation of wheel 14. Torque take-out assembly 22 is secured to astationary portion of the landing gear truck such as a bogie beam orother landing gear strut, such that torque take-out assembly 22 andstators 34 are prevented from rotating during braking of the aircraft.

Carbon and/or ceramic structures in the friction disks may operate as aheat sink to absorb large amounts of kinetic energy converted to heatduring slowing of the aircraft. Heat shield 40 may reflect thermalenergy away from wheel well 18 and back toward rotors 32 and stators 34.With reference to FIG. 1A, a portion of wheel well 18 and torque bar 24is removed to better illustrate heat shield 40 and heat shield sections42. With reference to FIG. 1B, heat shield 40 is attached to wheel 14and is concentric with wheel well 18. Individual heat shield sections 42may be secured in place between wheel well 18 and rotors 32 byrespective heat shield carriers 44 fixed to wheel well 18. Air gap 46 isdefined annularly between heat shield sections 42 and wheel well 18.

Torque bars 24 and heat shield carriers 44 can be secured to wheel 14using bolts or other fasteners. Torque bar bolts 48 can extend through ahole formed in a flange or other mounting surface on wheel 14. Eachtorque bar 24 can optionally include at least one torque bar pin 50 atan end opposite torque bar bolts 48, such that torque bar pin 50 can bereceived through wheel web hole 52 in web 20. Heat shield sections 42and respective heat shield carriers 44 can then be fastened to wheelwell 18 by heat shield fasteners 53.

With reference to FIG. 2, one or more of the brake components describedherein may be made using a field assisted sintering technique (FAST)device 200. FAST is also commonly referred to as plasma activatedsintering (PAS). FAST is a technique that employs temperature, pressure,and high voltage to rapidly sinter powders into monolithic materials. Inessence, FAST is a technique for pressure-assisted sintering activatedby electrical discharges between powder particles. Brake components maybe made using FAST to form the components using a mixture 212 of ceramicpowder and fibers to form a ceramic matrix composite (CMC) in a shorttime period.

In various embodiments, the fibers may comprise chopped fibers. Mixture212 is thus also referred to herein as CMC mixture 212. Examples ofsuitable fibers for use in mixture 212 may include carbon fibers, aramidfibers, silicon carbide fibers, or other types of fibers. Fiber filamentdiameters tend to be similar between different types. Fiber filamentsmay have diameters of substantially 5 μm (0.0002 in), 10 μm (0.0004 in),20 μm (0.0008 in), 50 μm (0.002 in), or 100 μm (0.004 in), for example.In that regard, fiber filament diameters may range from 7 μm (0.0003in)-15 μm (0.0006 in), 5 μm (0.0002 in)-50 μm (0.002 in), or 3 μm(0.0001 in)-100 μm (0.004 in). Length for chopped fiber may have alength ranging from 3.2 mm (0.125 in)-50 mm (2 in), 2.5 mm (0.1 in)-100mm (4 in), or 2 mm (0.07 in)-254 mm (10 in). Fiber preform lengths mayscale with the graphite mold up to the mold diameter.

In various embodiments, the fibers may be treated with an interphaselayer applied to inhibit fiber sintering to the ceramic matrix. Examplesof the interphase layer may include pyrolytic carbon or boron nitride.The addition of the interphase layer to the fibers may improve fracturetoughness relative to other composites prepared using FAST without sucha coating.

In various embodiments, mixture 212 may also include ceramic material inthe form of ceramic powder. Suitable ceramic powders may include SiC,B₄C, and/or Si₃N₄, TiB₂, or other oxides and/or borides, for example. Arange of particle sizes may be employed in the ceramic powder used tomake the CMC brake components of the present disclosure. The particlesize of the ceramic powder is also referred to herein as powder size.Typically, powder sizes in the micrometer or nanometer ranges areappropriate for FAST processing. For example, a micron-sizedboron-carbide powder may be selected when the manufacturing tools arenot suited to operate on nano-sized powders without the powders escapingfrom a die or mold. When chopped fiber is included in mixture 212, anano-sized powder may infiltrate into the fiber more readily than themicron-sized powder. The powder size may include a particle sizedistribution such as a bimodal particle distribution. Powder size maythus be selected based on desired grain size with smaller powder sizesyielding smaller grain sizes. For example, nano-sized powder yields asmaller grain size than micrometer-sized powder. The grain size mayimpact the thermal properties of the finished component. Particleuniformity may vary. For example, particle uniformity may vary indiameter by +/−80%. Particle size may also vary according to a Gaussiandistribution or by other industrially accepted variances.

In various embodiments, the upper size limit for powder may be definedby the inter-filament distance in a given tow bundle. This varies, butwill be something on the order of the filament diameter, which may besubstantially 5 μm (0.0002 in), 10 μm (0.0004 in), 20 μm (0.0008 in), 50μm (0.002 in), or 100 μm (0.004 in), for example. Minimum size may begoverned by commercial availability and the issues with potential escapefrom the graphite die if the powder is too small. For example, minimumpowder sizes may be on the order of 10 nm (4×10⁻⁷ in), 50 nm (2×10⁻⁶in), 100 nm (4×10⁻⁵ in), 500 nm (2×10⁻⁵ in), 5 μm (0.0002 in), 10 μm(0.0004 in), 20 μm (0.0008 in), 50 μm (0.002 in), or other suitablesizes.

In various embodiments, FAST device 200 may include a ring mold 214.Ring mold 214 may be an annular mold suitable for forming circular orannular CMCs. Ring mold 214 may be formed from various die materialsincluding graphite, refractory metals, ceramics, or other suitablematerials. Although a ring mold 214 is shown for exemplary purposes,other die shapes may be suitable for making non-circular brakecomponents.

In various embodiments, FAST device 200 may also include at least onepunch 210 to engage ring mold 214 along an inner diameter and applypressure during the FAST process. Punch 210 may thus be anelectronically or hydraulically actuated piston suitable for applyingsubstantial force to a heated material. For example, punch 210 may apply1,400 kN, 1,200 kN-1,600 kN, 1,000 kN-2,000 kN, or 800 kN-2200 kN offorce to CMC mixture 212 by actuating within an inner diameter of ringmold 214 and compressing CMC mixture 212 along the axis of ring mold214. In that regard, ring mold 214 may be well suited for use in formingannular or disc-shaped brake components such as friction disks.

In various embodiments, FAST device 200 may further include an electrode208, which may be graphite, coupled to and/or in electroniccommunication with punch 210. An electrode 206, which may be brass, maybe coupled to and/or in electronic communication with graphite electrode208. Graphite electrode 208 may thus be disposed between punch 210 andbrass electrode 206. A copper plate 204 may be coupled to and/or inelectronic communication with brass electrode 206. Although copper,brass, and graphite are identified for illustrative purposes, variousmetallic or otherwise conductive materials may be used to form theelectrodes of FAST device 200.

In various embodiments, transformer 216 may be in electroniccommunication with copper plate 204 to provide electrical current tomixture 212. Heat may be generated for the FAST process by dispersingelectrical current through the electrodes, ring mold 214, punch 210,and/or mixture 212. An induction coil 202 may be disposed about ringmold 214 to provide inductive heating to CMC mixture 212, thoughresistance heating by dissipating electrical current through electrodes,ring mold 214 and mixture 212 may provide sufficient heat fordensification absent induction coil 202 in various embodiments. Directheating through resistance heating or otherwise may enhancedensification over grain growth. Direct heating may further allow forfast heating and cooling rates, promote diffusion during the FASTprocess, and allow for the intrinsic properties of nano and micropowders to remain present in their fully dense product.

With reference to FIGS. 3A and 3B, an exemplary process 300 is shown formaking CMC brake components, in accordance with various embodiments.Process 300 may be completed using a FAST device 200 as disclosed inFIG. 2. Graph 301 depicts the various changes in temperature, pressure,and CMC density over the course of process 300. Process 300 may includemixing and/or depositing a mixture 212 into a ring mold 214 (Step 302).Mixture 212 may comprise ceramic powder and fibers, as described above.FAST device 200 may increase pressure applied to the mixture byactuating punch 210 to press against the mixture (Step 304). Step 304may be performed over period 305. The pressing force applied by punch210 may be substantially 100 tons (90,700 kg), 150 tons (136,078 kg),200 tons (181,437 kg), or another suitable pressing force.

In various embodiments, the FAST device may pulse electrical dischargesacross the mixture (Step 306). Step 306 may be performed over period307. The pulsed electrical current may flow through the ceramic powderalong the boundaries of the ceramic particles making up the ceramicpowder and, as a result, generate pulsed plasma between particles of theceramic powder. Pulsed current may be applied using direct current. Atypical cycle time for the CMC process may span 10 minutes, 15 minutes,or 20 minutes, for example. Current levels for the electrical pulses inFAST device 200 may vary depending on the machine. For example, thecurrent levels may range from 2,000 A-20,000 A, 1,000 A-25,000 A, or 500A-30,000 A. FAST device 200 may also operate with electronic energylevels of substantially 140 kVA, 200 kVA, or 240 kVA, for example. FASTdevice 200 may increase the temperature in the mold using resistanceheating or other direct heating techniques described herein. FAST device200 may apply pressure for final densification of the mixture (Step308). Step 308 may be performed over period 309. Pressure may be appliedusing punch 210 as described above. Appropriate maximum heatingtemperatures may be selected based on the ceramic and fiber selected formixture 212. Examples of appropriate maximum temperatures may includesubstantially 3000° C. (5432° F.), 2600° C. (4712° F.), 2400° C. (4352°F.), 2200° C. (3992° F.), or 2000° C. (3632° F.). The term substantiallyas to describe quantitatively measurable characteristics herein such astemperature and pressure shall refer to a variation in thequantitatively measurable characteristic ranging by +/−5%.

In various embodiments, the FAST device may reduce the voltage and thepressure at completion of the FAST process (Step 310). Step 310 may beperformed over period 311. The resulting CMC brake component may beoperated on further using milling, machining, or other techniques torefine the finished product. A suitable time to complete process 300 maybe 1 hour, 2 hours, 5 hours, 10 hours, 20 hours or any other suitabletime. The CMC FAST process may thus yield a CMC brake component in aperiod on the order of hours rather than days or weeks.

The FAST process may cause the ceramic particles to undergovaporization, solidification, volume diffusion, surface diffusion,and/or grain boundary diffusion. As a result, the CMC brake componentsmade using the processes and systems described herein may have a dense,monolithic grain structure. The dense, monolithic grain structure mayhave controlled proportions of ceramic to fiber resulting in a superiorupper use temperature relative to components made using MI, for example.The CMC brake components can also be completed in a shorter period thansimilar components made using CVI or PIP.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosures.

The scope of the disclosures is accordingly to be limited by nothingother than the appended claims, in which reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” Moreover, where a phrase similar to“at least one of A, B, or C” is used in the claims, it is intended thatthe phrase be interpreted to mean that A alone may be present in anembodiment, B alone may be present in an embodiment, C alone may bepresent in an embodiment, or that any combination of the elements A, Band C may be present in a single embodiment; for example, A and B, A andC, B and C, or A and B and C. Different cross-hatching is usedthroughout the figures to denote different parts but not necessarily todenote the same or different materials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”, “anexample embodiment”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiment

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element is intended to invoke 35 U.S.C. 112(f)unless the element is expressly recited using the phrase “means for.” Asused herein, the terms “comprises”, “comprising”, or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A ceramic matrix composite (CMC) brake componentfor an aircraft, comprising: an annular disc comprising: a ceramicmaterial having a monolithic grain structure, wherein the ceramicmaterial comprises at least one of SiC, B₄C, or Si₃N₄; and choppedfibers disposed within the ceramic material, wherein the chopped fibersare coated with an interphase layer, wherein the chopped fibers compriseat least one of carbon fibers or SiC fibers.